This invention relates generally to an image recording apparatus such as an optical printer, a copying machine or the like of type utilizing a photo-sensitive recording medium, and more particularly, to an exposure system for the photo-sensitive recording medium.
Referring to FIG. 1 of the drawings, there is schematically shown a usual of general copying machine for copying image information on an original to a photo-sensitive recording medium. The copying machine comprises a transparent glass platen 51 movable in a direction indicated by an arrow A. An original 52 having carried thereon image information is placed upon the platen 51. Light from a light source 53 scans the information side of the original 52, while the original 52 as well as the platen 51 is moved in the arrowed direction A. Light reflected by the original 51 is directed toward a photo-sensitive recording medium 54 transported in a direction indicated by an arrow B, so that the recording medium 54 is exposed to the light. The recording medium 54 is then developed by a pressure developing unit 55.
For the arrangement illustrated in FIG. 1, it is required that the recording medium 54 is exposed to the light while being maintained horizontal. To this end, in general, a table 56 is provided for enabling the recording medium 54 to rest upon an upper surface or a resting surface of the table 56. The recording medium 54 moves in sliding contact with the resting surface of the table 56.
Usually, the resting surface of the table 56 is formed into a mirror surface or a white surface for the following reason. That is, the light transmitted through the recording medium 54 is reflected by the resting surface of the table 56, and the recording medium 54 is again exposed to the reflected light from the back side of the recording medium 54, thereby utilizing the light quantity effectively.
In connection with the above, the light emitted from the light source 53, reflected by the information side of the original 52 and shining upon the recording medium 54 at the exposure has such a deviation that the light quantity at each of opposite end regions on the recording medium 54 in the main scanning direction is less than that at a central region on the recording medium 54. As a consequence, when the recording medium 54 is exposed to the light, the central region on the recording medium 54 is exposed sufficiently to the light, but the opposite end regions on the recording medium 54 become insufficient in exposure. When the exposed recording medium 54 is developed by the pressure developing unit 55, an exposure difference tends to occur between the central region and the opposite end regions of the recording medium 54.
In order to compensate for the exposure difference, such a measure has usually and conventionally been taken that a slit 57 is arranged immediately above the recording medium 54. The slit 57 is narrow at its longitudinally central region, but is wide at opposite end regions, thereby correcting the light quantity distribution.
In the conventional exposure system, however, provision of the slit for correcting the deviation in the exposure quantity with respect to the recording medium complicates the construction and increases the number of component parts, resulting in an increase in the cost.